Measuring the Neutron and 3 He Spin Structure at Low Q 2 Vincent Sulkosky

1. Experimental Overview Analysis Overview and Progress The neutron GDH Experiments at JLab Hall A GDH Sum Rule (Q2 = 0) The goal of Jefferson Lab experiment E97-110 is to study neutron and 3He spin structure by performing a precise measurement of the generalized Gerasimov-Drell-Hearn (GDH) integral at Q2 between 0.02 and 0.3 GeV2. The Experiment was run in summer 2003 in Hall A. Beam line: beam polarization, current calibration, energy measurements, etc. Elastic analysis and background Detector calibrations and efficiencies: VDC, gas Cherenkov, and shower calorimeters Spectrometer optics and acceptance Target polarimetry Asymmetries and cross sections Radiative corrections Experimental Setup Sum Rule Static Properties d = + 2% d = + 0% d = - 2% d = - 4% measured theory well known • Polarized electron beam, average Pbeam ~ 75% • Current ~ 1-12 mA • Hall A polarized 3He target (as effective neutron target) • Scattered electrons detected by Hall A High Resolution • Spectrometer coupled with a septum magnet (inclusive • reaction). • Septum magnet: horizontal bending dipole magnet that • enabled detection of electrons at 6 and 9 degrees. • Can be used to check theory or measure static properties. • s1/2 and s3/2: cross sections for photoproduction with two • different photon polarizations. • Can begeneralized for nonzero Q2. Generalized GDH (Q2 > 0) Carbon foil position reconstruction along the beam line at four different momentum settings within 4% of the elastic peak. The vertical lines represent the nominal foil positions. • Replace photoproduction cross sections with • electroproduction (virtual photons). • Previous JLab experiment E94-010: • Measured generalized GDH on neutron with Q2 between 0.1 • to 0.9 GeV2. • Studied transition between strong interaction’s partonic to • hadronic descriptions. Results did not agree well with Chiral • perturbation theory above 0.1 GeV2. • Present work, JLab experiment E97-110: • Benchmark test of Chiral perturbation theory (cPT) in a • region where it should be valid. • Extrapolate to the real point (Q2 = 0). Floor layout in Hall A. The septum magnet. Plot of 3He elastic asymmetry showing the four different target and beam configurations. Simulation: 1.39%. Preliminary data analysis: (1.403 0.044)% (stat. only). Energy deposited in total shower calorimeter after calibration. Polarized 3He Target 3He as an effective n target: Expected Results Target Apparatus and Performance 3He = 3He n Target performance during experiment E97-110. Effective polarized neutron target Polarized RB and 3He 220 oC • Optical pumping of Rb atoms • Spin exchange between Rb atoms and • 3He nuclei • Target cells: 40 cm, ~ 10 atm • Highest polarized luminosity in the • world: up to 1036 cm-2 s-1 50 oC Polarized 3He only 3He standard target cell. Polarized target setup. • Longitudinally and transversely polarized target. • Ptarg = 38.5% (from on-line analysis). • Two independent polarimetries: NMR and EPR. Electron Beam Scattered Electrons E97-110 expected accuracy for the neutron generalized GDH integral. The red circles show the E94-010 results. The blue circles show the Q2 range, and the blue band shows the expected systematic uncertainty. The vertical axis has been normalized to the neutron value at the real photon point (233.2 mb). Special cell designed for forward angle detection. Measuring the Neutron and 3He Spin Structure at Low Q2 Vincent Sulkosky for the JLab Hall A Collaboration College of William and Mary, Williamsburg VA 23187